1. Field of the Invention
This invention relates to the grouting of offshore structures.
2. Description of the Prior Art
Offshore structures or rigs have come into increasing use in recent years to support platforms for drilling of oil and gas wells and for producing oil and gas from such wells. Such structures may be erected in water from comparatively shallow depths up to several hundred feet deep. A variety of forms of structure and methods of construction of such platforms have been utilized. One such method which has been found to be particularly desirable in deep water is that which is illustrated, for example, in U.S. Pat. No. 3,209,544 to Borrmann, in which the legs of the structure are fabricated and assembled on shore. The legs are hollow, and may be sealed to make the structure buoyant, so that it can be towed out to the desired offshore location. Valves in the legs are opened to allow flooding with sea water, so that the leg structure will sink in a vertical position and settle onto the bottom. As the legs sink they fill with water up to the water level of the sea. It will be appreciated that the legs will sink into the ocean bottom a distance dependent upon the weight of the structure and the softness of the ocean bed.
A platform which is built only on such legs would have a high degree of instability, particularly in heavy storms. It has, therefore, been the practice to more rigidly connect the structure to the ground by driving hollow steel pilings down through the legs, which then become jackets for the pilings.
When the piling has been fully driven (usually to refusal), it has been the practice to fill the annulus between the piling and the jacket with a grouting material which solidifies in place. This increases the rigidity and, therefore, the strength of the structure by increasing the surface area and strength of the connection between the piling and the jacket. It also helps to keep out water so as to prevent corrosion of the piling.
Various methods have been utilized for grouting such structures. One method, as shown in the aforesaid Borrmann patent, for example, requires the use of a seal member at the bottom of the annulus. In this method the grouting material is pumped into the bottom of the annulus and rises upwardly therein to the top. This method usually requires the use of divers, and in addition, it often fails to produce fully satisfactory results because water cannot be effectively excluded from the annular space so that the grounting material becomes diluted and difficult to set.
Evans et al, in U.S. Pat. No. 3,492,824, describe a method comprising injecting air into the top of the annulus to expel water through a nipple at the bottom of the annulus, and then injecting grouting material through the bottom nipple. The grouting material is supposed to rise up through the annulus to above the water line, displacing air out the top. As a practical matter such a system would be very unsatisfactory. The ocean bed is normally soft and porous at the bottom of the jacket so that as soon as enough grouting material is pumped in to overcome the hydraulic head of the overlying sea water, the grouting material would begin to run out the bottom of the jacket and would be lost. Thus, it would be necessary to utilize some kind of seal or closure at the bottom of the annulus to hold the grouting in.
Evans et al also disclose a method whereby air is injected into the nipple at the bottom of the annulus to drive the water upwardly through the annulus out the top. It is apparent that such a system would be extremely inefficient in expelling water, since the air, being lighter, will rise up through the water. The same problem of losing grout out the bottom would also exist in this method.
Blount et al in British Pat. No. 1,307,181, issued Feb. 14, 1973, disclose another grouting system in which the grouting material is injected through nipples at the bottom of the annulus. Blount uses water to wash out mud from the location of Blount's injection nipples upwardly; but, Blount makes no attempt to remove water or mud from below the injection point. Furthermore, Blount's annulus is filled with water at the start, which must be expelled upwardly by the rising grouting material. Thus a large excess of grouting material would be necessary in order to insure that all of the water is expelled out of the top of the annulus.
Olsen and Bassett disclose, in their U.S. Pat. No. Re. 28,232, a reissue of U.S. Pat. No. 3,601,999, a system which avoids many of the problems encountered in other grouting systems. U.S. Pat. No. 3,832,857 to Bassett is an improvement over that system.
See also:
U.S. Pat. Nos.
1,013,758--Fox et al, issued Jan. 2, 1919, for "METHOD OF APPARATUS FOR APPLYING PROTECTING COVERING TO PILES:"
1,084,063--Bignell, issued Jan. 13, 1914, for "MEANS FOR FORMING UNDERGROUND FOOTING FOR PILES AND CAISSONS:"
1,729,422--Gleasner, issued Sept. 24, 1929, for "METHOD OF CLEARING AND FILLING TUBULAR PILES FOR FOUNDATIONS;"
1,753,440--Miller, issued Apr. 8, 1930, for "METHOD OF DRILLING WELLS IN GAS FORMATIONS;"
3,011,547--Holbert et al, issued Dec. 5, 1961, for "METHOD OF PREVENTING LOSS OF GASEOUS DRILLING FLUID;"
3,100,525--Smith et al, issued Aug. 13, 1963, for "CEMENTING:"
3,114,419--Perry et al, issued Dec. 17, 1963, for "METHOD FOR POLYMERIZING LIQUID RESIN-FORMING MATERIALS;"
3,152,641--Boyd, issued Oct. 13, 1964, for "METHOD FOR POLYMERIZING RESIN-FORMING MATERIALS IN SUBTERRANEAN AREAS;"
3,187,513--Guild, issued June 8, 1965, for "METHOD OF DRIVING PILES;"
3,196,946--Lauffer, issued July 27, 1965, for "AIR METHOD OF CEMENTING WELLS;"
3,213,629--Manning, issued Oct. 26, 1965, for "APPARATUS AND METHOD FOR INSTALLATION OF A PILE-JACKET ASSEMBLY IN A MARINE BOTTOM;"
3,597,930--Rochelle, issued Aug. 10, 1971, for "METHOD AND APPARATUS FOR REINFORCING IN SITUS IN PILE CASING;"
3,811,289--Bassett, issued May 21, 1974, for "METHODS OF GROUTING OF OFFSHORE STRUCTURES;" and
3,878,687--Tragesser, Jr., issued Apr. 22, 1975, for "GROUTING OF OFFSHORE STRUCTURES."
FOREIGN PATENTS
Austrian Pat. No. 23,039--Josef Vincent Brejcha, issued Feb. 10, 1906, for "FLUSH JOINT FOR BORE HOLES;"
Swiss Pat. No. 180,901--Eugene Frote, issued Feb. 1, 1936, for "PROCESS FOR THE CONSTRUCTION OF EXPANDED BASE PILES, CAST IN THE GROUND;"
German Pat. No. 286,333--August Wolfholz Preszzementbau, issued Apr. 1, 1913, for "PROCESS FOR CASTING CONCRETE PILES IN THE GROUND, BY MEANS OF A CASING AND COMPRESSED AIR;" and
British Pat. No. 674,809--Lionel Ignacio Viera Rios, issued July 2, 1952, for "METHOD OF AND APPARATUS FOR SINKING CONCRETE, CEMENT OR THE LIKE PILES IN GROUND HAVING AN EXCESSIVE MOISTURE CONTENT".
The present invention of grouting is an improvement over the piror art patents for use with submerged piles for offshore rigs set in deeper water.